For the OP, do check the wear in the bushing. If they get too much clearance, the sheave can tilt off to one side a bit. This both accelerates the wear and eventually the rim of the sheave contacts the sides of the sheave box, greatly increasing frictional losses. If this is the case, pressing the old bushes out and new ones in is a DIY job if you have a decent sized vise or a small press available. The bushes can be purchased at any seal and bearing shop, and they are inexpensive.
As to lubrication, well, Oilite scintered bronze bushings do pretty well on their own for a while, but seem to loose lubricity over time. Unlike some of the posters upthread, I've used small amounts of marine
grease o n the pins on all such sheaves for several decades, and not had the horrible results posited. In fact, they have thrived! YMMV.